The present invention relates to a method for controlling a powertrain and more particularly to a method for controlling a powertrain having multiple torque sources.
Engines in current production automobiles are typically sized to meet certain performance requirements. For normal city and highway driving, a relatively large capacity engine is operated at low loads (e.g. at a partial torque output), which in turn leads to low engine efficiency and therefore high fuel consumption. Several approaches have been proposed to modify the powertrain of a vehicle such that it results in higher engine efficiency during low loads. One such solution is disclosed in commonly assigned U.S. Pat. No. 6,306,056 to Moore, herein incorporated by reference as if fully set forth herein. ""056 to Moore discloses a hybrid vehicle having multiple separate torque sources coupled to a conventional automatic transmission. When the vehicle is operated at a relatively low rate of speed, only one of the torque sources is employed to propel the vehicle. When the torque demand exceeds the single torque source""s maximum torque output, a second torque source is activated and engaged to the transmission, and synchronized with the first torque source.
However, typical automatic transmissions attached to traditional internal combustion engines reduce gear shifting in order to maintain a higher fuel economy. In a powertrain with multiple torque sources, as described above, initializing, starting, and synchronizing additional torque sources is less fuel efficient than shifting gears within the transmission.
A method for controlling a powertrain in a motor vehicle having a first torque source and a second torque source each providing a torque output to a transmission is provided. The method includes determining a vehicle speed and a current gear selection of the motor vehicle. A threshold value is calculated from the vehicle speed and the current gear selection. An accelerator position of the motor vehicle is then determined. An accelerator position rate of change is calculated from the accelerator position. The accelerator position rate of change is compared to the threshold value. The torque output from the first torque source is increased if the accelerator position rate of change is less than the threshold value. However, the transmission is downshifted if the accelerator position rate of change is greater than the threshold value.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.